Friction lining



UNITED STATES I PATENT OFFICE 2,012,259 mIorroN LINING Harry B. Denman,Pontiac, Mich.

No Drawing. Application December 16, 1932,

Serial No. 647,701

Claims.

. The present invention relates to a friction composition and in itsmore specific aspect the invention is directed to a friction liningadapted to be utilized as a braking medium.

5 The friction composition forming the subject matter of the presentinvention contains talc as one of its essential constituents, andparticularly that type of talc occurring in the foot hills of theAdirondack Mountains and belonging to the Grenville series ofcrystalline limestones of the pre-Cambrian age. What is known asGouvemeur talc occurs in this formation.

As to the nature of talc and its varieties, it is desired to refer toBulletin 259, May 1925, of the New York Museum, wherein it is 'stated:'

Talc is a mineral of variable habits and qualities; and its uses varywith its characteristics, chemically, it is all one and the samematerialhydrated magnesium silicate. It occurs in two 2 general forms:as a primary deposit from solution, and as a secondary product thatresults very commonly from local alteration of anhydrous magnesiumsilicate, such as tremolite (CaMga(Si03)4 and enstatite (MgFe(SiOa)2).

a mica in appearance, has certain definite'physical properties, and inchemical composition comes close to the proportions demanded by theformula, that is, silica 63.5%, magnesia 31.7% and water 4.8%(Mg3(SlOz)4.HzO). Secondary talc has no well defined physical structurebut adopts the structure of the mineral from which it has originated,granular, fibrous or massive, as the case may be. It is likely to besomewhat impure, varyunaltered remnants of the parent substances.

Talc and its formation is also described in Bulletins 223 and 224, Julyand August, 1919, of the New York State Museum, as follows:

"Nature of talc.-The mineral is both a primary deposit from solution anda secondary product resulting from the alteration of an anhydrousmagnesium silicate of the 'amphibole or pyroxene groups (tremolite, fromwhich the 45 Gouverneur fibrous talc originates is an amphibole) Thetale in the Edwards (now referred to as Gouvemeur) district isprincipally secondary and psendomorphic talc, derived by alteration ,of50 tremolite whose physical structure is still re- Primary talc has ascaly or foliated habit, likeing with conditions, and particularly tocontain tained. The talc occurs in small elongated to squarishparticles, made up of many parallel fibres; and these fibrous aggregatesare intergrown so as'to constitute a solid mass of schistose appearance.To the unaided eye the rock ap- 5 pears homogeneous, but when examined'more carefully with the aid of the microscope it is usually observed tocontain more or less residual tremo lite that has not succumbed to thealteration process. "Foliated or crystal talc 10 is present to a minorextent in most of the occurrences in the Edwards (Gouverneur) district.

It occurs in seams and other openings, where it has been depositeddoubtless by waters circulating thru the deposits, to which theconversion of 15 tremolite into fibrous tale is ascribed; that some ofthe tale should be taken into solution and reprecipitated apart seemsonly natural.

From the above, it is clear that talc mayocour in threevarieties-massive or granular, o fibrous and foliated, and in theGouverneur district the three varieties are found.

The form of talc which has been found eminently desirable as aconstituent of the friction composition forming the subject matter ofthe present invention is the short fiber talc, and pref erably thatoriginating from the Arnold Mine located adjacent to Gouverneur, NewYork, and operated by the W. H. Loomis Talc Corporation.

The short fiber talc above referred to analyzes a as follows:

Silica 56.54%

i Fe2Oa+A12Oa 1.04% MnO -Occasional trace MgO -l 30.74% 35 CaO u e"6.25% C02 .83% Loss on ignition 4.60%-

A recast analysis of the above is: v 40 Per cent Calcium silicate(CaSiOa) 11.00 Talc (HzMgzKSiOaM) n. 85.00 Calcium carbonate (CaCOa)1.88 Water at 212 F .50

The talc has the following physical properties: Specific gravity'2.80-3.1 Hardness 4-5 Fusion point 2615 F. Dielectric strength 30 voltsper mil.

Mineralogically speaking, the tale typified by the Gouverneur shortfiber tale is an alteration product of tremolite (amphibole) having theformula CaMga(Si0s)4. The alteration consists in the removal of calciumand the substitution of water so that the alteration product is afibrous talc containing more or less tremolite. The amount of calciumsilicate in the talc depends on the state of alteration from tremolite,and usually varies not more than a point either way from 11%. The talecoming from the Arnold Mine is very constant in that respect. Theanalysis above set forth shows that the rock carries about 6.25% calciumwhich after deducting the amount necessary to combine as a carbonatewith CO2 yields between 10 and 12% in different analysis to be combinedas a silicate. Of course, the percentage composition of the rock is arecast one based on the chemical analysis. It is, therefore, obviousthat while the percentage of tremolite present in the Gouverneur shortfiber talc may vary, it is usually around the above figure and the taleis, therefore, a fairly pure one.

The product produced from the short fiber tale of the Gouverneurdistrict, the properties and composition of which have been set forth,may be considered as a talc carrying a proportion of tremolite. TheGoverneur fibrous talc is of course to be distinguished from foliated orbestos fiber is in use, it very frequently is heatedslippery talc.Fibrous and massive tales lack slip, and this is also true of thegranular variety. The short fiber Gouverneur talc has a hardness ofabout 4 to 6, depending on how far the alteration of the parent materialhas proceeded. The foliated talc, due to its slipperiness, has a muchlower coefficient of friction than the fibrous talc, and since thefoliated talc is softer than the fibrous talc the latter gives a betterwear factor. The difference between short fiber talc. and foliated taleis quitedistinct and easily seen. In addition to the physical propertiesabove set forth which distinguish the two varieties of talc, they may bedistinguished by merely rubbing a finely powdered sample of each varietybetween the fingers. The foliated talc and the massive steatite have agreasy feel and are shiny, while the finely divided short fiberGouvemeur tale is smooth and lacks the greasy feel and shiny appearance.

' The tale typified by Gouverneur talc has given particularlysatisfactory results, and therefore it is the preferred talc componentof the friction composition herein disclosed. However, other talesoriginally occurring in the fibrous state and having high coefiicientsof friction when finely divided may also be used, although-the resultsare not quite so satisfactory.

The fibrous tale in 'its original condition resembles some forms ofasbestos and is therefore known as asbestine.

The above described talc and/or asbestine when finely ground, forexample so that 98%Ithereof passes through a 325 mesh sieve, forms apowderlike mass and to all intents and pu p ses is, as compared toground-up asbestos, a non-fibrous material. In other words, if asbestosis ground up'to a fibrous state, due to the inherent character-of thematerial, that is the strength, toughness and pliability of .its fibres,the fibrous'state is maintained. Talc on the contrary forms apowder-like mass. To the naked eye, when asbestos fibers are finelyground .up the fibers still appear fibrous. On the contrary, when theshort fiber talc and asbestine is finely ground up, to the naked eye thetale. appears non-fibrous,- although underfthe microscope it is somewhatfibrous, showing very short and minute fibers with a large proportion ofthe fibers broken down to form a granular mass. The term non-fibrous asapplied to short fiber talc and asbestine is used in thesense above setforth. However, the difference between the two materials may be perhapsbetter brought out by describing their action in a friction compositionwhile in actual use. When asbestos is mixed with a binder such asrubber, the asbestos fibers do not blend thoroughly but remain visible,giving the composition a fuzzy appearance. The composition is nothomogeneous and the asbestos fibers tend to form small agglomerates orlumps which may be picked out of the friction composition quite readily.The presence of the small agglomerates or lumps makes the compositionnon-homogeneous and materially decreases the effective contact surfaceof the composition, resulting in a corresponding decrease in brakingpower.

When finely divided talc or asbestine is mixed to a temperature varyingbetween 700 F. and 800 F. At that temperature the asbestos fiberundergoes a chemical or physical change, and it becomes hard enough toscore the braking drum producing in some instances inefficient brakingconditions, and the tendency of the drum to score is magnified after thebrake lining has been in use for sometime. Finely ground talc typifiedby Gouverneur .talc does not undergo that change, except at much highertemperatures not usually attained under ordinary conditions, and there.-fore scoring of the brake drum is substantially eliminated.

As stated, the tale is reduced to a finely divided state. While it isnot desired to be lim- .ited to any particular mesh size, in general itmay vulcanizable fatty residue, reclaimed rubber, or

artificial rubber known as Duprene, the latter being chloroprene orpolymerization products thereof, as hereinafter set forth. Thechloroprene polymerization products may be mixed with rub-. ber and havea friction constituent of any type dispersed therethrough. When using a.mixture of rubber and chloroprene, the mixture together with thefriction constituents dispersed therethrough may be vulcanized. Thepreferred friction constituent is the herein disclosed tale.

The friction composition may have mixed therewith a waterproofing agentusually resins and/or waxes. By-varying the amount of the resin, andparticularly rosin and/or wax, the coefiicient of friction of thecomposition may be varied over quite a wide range. The wax used inmaking the composition also facilitates the -mixing thereof and servesas a'waterproofing agent in the'finished product. Various waxes such asmineral, hydrocarbon and vegetable waxes may be used, it not beingdesired to be limited to any particular wax. For example, there may beusedozokerite, beeswax, Mont-an wax, paraflin'wax or ceresin wax,paraffin wax being preferred.

The friction composition mix prior to vulcanization has present avulcanizing agent. This may include the ordinary inorganic vulcanizingthe 'diphenylguanidine.

compounds which usually contain sulfur, or an organic accelerator may beused to decreasethe time of vulcanization. Usually, there is alsopresent compounds functioning as'an activator for the particularvulcanizing agent or accelerator used. For example, zinc oxide may beused as an activator. Lime, magnesium oxide, or mixtures of the same,also may be present in the mix to assist in the vulcanization, althoughneither is essential, as both may be omitted without greatly affectingthe desirable characteristics of the finished product. Zinc oxide also,while desirable, is not absolutely necessary.

As an example of a suitable accelerator, diphenyl-guanidine may be used.However, it is obvious that other organic accelerators well known and onthe market may be substituted for The following is a specific example ofa suitable rmxr A master batch is made from rubber, rosin and anaccelerator. For example, the specific composition of the master'batchmay be:

Parts by weight Rubber -i Rosin 25 Accelerator 1 The amount ofaccelerator used may be varied,

depending on the type of accelerator used and the length ofcure-desired.

The rosin in the above example may be replaced in whole or part by asynthetic resin. Satisfactory results are obtained using a phenolformaldehyde condensation product produced by the Bakelite Corporationof New York and known as CEO-220. The resin is added preferably in thepowdered form, asin this form the incorporation into the batch isfacilitated.

Instead of using 25 parts of rosin in the master batch, the same may bereplaced by a phenola synthetic resin of which a phenolic formaldehydecondensation product is illustrativemay. be used in the master batchwhen the brake lining is used on trucks or other vehicles having arelatively low"speed;"In"'high"speed vehicles where excessive heat isgenerated, when the brakes are applied, it is desirable to use in themaster batch only the synthetic resin insteadof mixtures of the samewith. rosin. A portion of the master batch prepared a above, is mixedwith the talc or asbestine and a suitable example is as follows:

i or metal shoe.

present invention.

In making the complete mix, the following represents the preferred modeof procedure, and

gives the most satisfactory results. However,

the invention is not limited to the particular manner of mixing hereinsetforth.

The master batch is mixed separately, either in an internal type ofmixer or in a standard mixing mill. The rubber is first broken down torun smoothly, after which the waterproofing agent, for example rosin,and the accelerator are added as rapidly as possible. The entire mass isthereafter mixed thoroughly until the rosin is entirely blended into therubber. The batch is then sheeted out and allowed to cool.

The required amount ,of the master batch is placed on a mixing mill orin an internal mixer and warmed until it begins to run smoothly.

Thereafter, the finely divided talc or asbestine, together with a waxand suitable activators are added as rapidly as possible. In thespecific example given, the activating material comprises lime and zincoxide. The wax is preferably added during the early stages of the mixingto facilitate the blending of the mixed constituents. The sulphur isadded towards the end of the mixing period and allowed to mix just longenough to become thoroughly blended in the batch. The batch isthereafter sheeted out and allowed to cool.

The complete batch is warmed in the customary manner and passed througha sheeting calender to sheet it. out to the requiredthickness and width.The sheeted material is then ready for vulcanization, and incarrying-out the vulcanization the sheet of material may be placedbetween heated plates under pressure for a sufiicient time to allowvulcanization to occur. In the example given above, the materialis'vulcanized for twenty minutes'at 315 F. under a hydraulic linepressure of 2250 pounds per square inch. It is obvious that the time andtemperature of vulcanization. as well as the hydraulic pressure, may bevaried as desired. The degree of vulcanization may of course be variedto meet predetermined service conditions. In general, however, thevulcanization is carried to a point where .the vulcanized material willgive a test reading of 98 to 100v on a Shore durometer.

The sheeted mix may be vulcanized alone or it may be vulcanized to abase'material to form a friction facing. The base material may consistof another rubber compound or a rubber and fabric combination, or fabricwith and without reinforcements, or it may consist of a metal strip Thebraking element is made up of two distinct materials, a facing materialto function as a braking surface, and a base material such as a metalstrip or the like function- It is desired to point out that theparticular method of mixing the ingredients may be considerably varied.For example, instead of making a master batch and then compounding thiswith other ingredients, all the materials may be mixed in one operation.Any method of mixing consistent with good manufacturing practice may beused, and this will depend in a measure upon the type of equipment whicha particular. rubber manufacturer has available. However, the twostepmethod of mixing has given very satisfactory results.

In the above examples illustrative of the preferred form of theinvention, the major constituents of the mix are finely dividedGouverneur talc and rubber, the Gouverneur talc or asbestine beingpresent in a predominating quantity. In the examples given, theasbestine may be replaced by a mixture of asbestine and foliated orslippery talc, the percentage of, the foliated talc running from aboutto 25% based on the weight of the asbestine. The important point is.that the foliated talc should not be added in a quantity sufilcient toimpair the braking efiiciency of the friction material. ,Stateddifferently, the coefiicient of friction should not be materiallyreduced. There may be mixed with the asbestine or talc other diluentsinstead of the foliated talc, as for example finely divided serpentine.ever, the predominating proportion of the friction ingredient orcomponent should always be a fibrous talc in a predominating proportion,and

45 preferably Gouverneur talc or asbestine.

It is to be understood that the particular examples given are merelyillustrative of suitable mixes and are not by way of limitation. Thepercentage of .finely divided asbestine may be considerably below 65%and still come within the spirit of the invention. In the preferred formof the invention the asbestine which forms the major frictionconstituent should be present ina predominating proportion. .It may beas low at 50% and in some cases, depending on service conditions to bemet, even lower. However, it'is desired to point out that the finalproduct should be a homogeneous one, and in s cc should not form lumpsor agglomerates, or in other words it should have non-pittingcharacteristics.

In the-place of natural rubber there may be used synthetic rubber,commercially known as Duprene, manufactured by E. I. du Pont de Nemoursand Co. The preparation of this product is described in the Journal ofthe American Chemical Society for November, 1931'. Nieuwland, Calcott,Downing and Carter describe on pages 4197 to 4203 the polymerization ofacetylene in their article entitled Acetylene polymers and theirderivatives. 1. The controlled polymerization of acetylene; andCrothers, Williams Collins and Kirby discuss chloroprene and itspolymers in I. A new synthetic rubber: chloro elusive. The u-polymer ofchloroprene can be vulcanized like ordinary rubber. The vulcanizedproduct however has greater oil resisting and heat resisting propertiesthan natural rubber. Natural rubber swells considerably under the'action of oils, and this disadvantage is eliminated when using thea-polymer of chloroprene.

Any of'the artificial rubber products described in the above articles byNieuwland, Calcott, Downing and Carter or Carothers, Williams, Collinsand Kirby may be mixed with a friction constituent to produce a brakelining or other friction compositions. This phase of the invention isnot limited to the utilization of talc as a friction constituent and, asstated, other friction con stituents may be used in place of the tale.While it is preferred to use the a-polymer of chloroprene, otherpolymers, the production of which is described in the articles referredto, may be combined with a friction consituent such as talc andparticularly the short fiber talc 'or asbestine, the properties of whichhave been enumerated. The chloroprene products above described andparticularly the a-polymer may be mixed with rubber, and this mixturemay have dispersed therethrough a finely divided friction constituent,and particularly finely divided talc, it being preferred to use theshort fiber talc of the Gouverneur type, although other forms of talcsuch as foliated talc may be wholly or partly substituted therefor.

In place of the specific phenolic condensation product set forth theremay be added to the master batch any phenolic condensation product orany synthetic resin now on the market or disclosed in the prior artwhich will function to waterproof thefinal friction composition and/ormodify its coefilcient of friction.

The present application is a continuation-inpart of application SerialNo. 475,640, filed August 15, 1930.

What I claim is:

1. A homogeneous friction element free of fibrous material andcontaining as its essential ingredients, an organic binder, and apredominating proportion of fine divided asbestine.

2. A homogeneous friction element freeof fibrous material andsubstantially non-pitting in character containing as its essentialingredients vulcanized rubber and finely divided asbestine dispersedtherethrough, the latter being present in a predominating proportion.

3. A homogeneous friction element free of fibrous material andsubstantially non-pitting in character containing as an essentialelement an organic binder and at least 50% of finely divided asbestine.

4. A homogeneous friction element free of fibrous material andsubstantially non-pitting in character containing as its essentialingredients vulcanized'rubber and at least 50% of finely dividedasbestine dispersed therethrough.

5. A homogeneous friction element free of fibrous material andsubstantially non-pitting in character containing as its essentialingredients an organic binder-and a predominating proportion of finelydivided asbestine together with rosin and wax acting to modify thecoemcient of fric-' tion of the friction element.

6. A homogeneous friction element free of fibrous material andsubstantially non-pitting in character containing as its essentialingredients vulcanized rubber and finely divided asbestine inapredominating proportion dispersed therethrough together with rosin andwax acting to A $012,259 modify the coemcient of friction of thefriction element. 7. A substantially non-pitting homogeneous frictionelement characterized by the absence of agglomerates under serviceconditions, containing as its essential ingredients an organic binderand a predominating proportion of finely divided non-fibrous asbestos.

8. A homogeneous friction element containing as its essentialingredients an organic binder and a predominating proportion of finelydivided asbestine, said friction element being free of fibrous andfilamentous bodies adapted to cause pitting of the friction elementunder service conditions.

.9. A homogeneous friction composition com prising the vulcanizedproduct of a mixture of rubber, a predominating proportion of finelydi-- vided asb eetine and a synthetic resinhaving similarcharacteristics under heat as the phenolic formaldehyde condensationresins, said synthetic resin acting to modify the coefiicientof frictionof the composition, the latter being non-pitting in character.

10. A friction composition comprising the vulcanized product of amixture or rubber, a predominating proportiog of finely dividedasbestine, a teristics synthetic resin aving similar charac under heatas the phenolic formaldehyde condensation resins, and rosin, saidsynthetic resin and rosin acting to modify the coefilcient of frictionof the composition, the latter under service.

conditions being non-pitting.

v -EARRY B. DENMAH-v

